This invention relates to thioether-modified polymeric compositions which are particularly suitable for use as sealants for insulating glass.
The term "insulated glass" broadly refers to a structure comprising panes of glass, the faces of which are in spaced relationship, thereby providing between the glass panes a space which imparts insulating properties to the structure. In its most widely used form, two parallel panes of glass are positioned in spaced relationship by metallic spacers positioned around the perimeters of the panes, and indented a short distance from the edges of the panes, thereby forming a U-shaped channel in which the legs of the U comprise the interior surface edges of the panes and the base of the U comprises a side of the spacer. Typically, the spacer is a hollow member filled with a water absorbent material, for example, a molecular sieve, to keep the enclosed air space between the glass panes dry. In such a structure, the aforementioned U-shaped channel is filled with a sealant, generally a polymeric composition, which must have a certain combination of properties for satisfactory use.
The sealant must have a very low water vapor transmission (WVT) rate so that moisture is prevented from entering the dry space between the panes of glass. The presence of moisture in the space tends to reduce the insulating value thereof. Moisture in the space can also condense on the panes of glass and create visibility or aesthetic problems. If the sealant does not have a satisfactory low WVT rate, the capacity of the water-absorbent material in the hollow spacer will be exceeded, and moisture will find its way into the space.
The sealant should be thermally stable and form an excellent bond with glass which is not degraded over long periods of time under normal conditions of use, which generally include exposure to sunlight, moisture, and large changes in temperature.
Furthermore, the sealant itself should not be a source of material which enters the space between the panes of glass. Should one or more constituents comprising the sealant volatize into the space, fogging, often referred to as "chemical fogging," of the glass panes may result.
Temperature variation will tend to cause contraction and expansion of the insulated glass structure. Therefore, the sealant should have an elongation of at least 100%, and preferably an elongation of at least 200%.
The sealant should also resist degradation due to contact with conventional caulks and putties.
At present, the most widely used insulated glass sealants are prepared from polysulfide liquid polymers, selected plasticizers, and glass adhesion promoters such as silanes. Generally, polysulfide type sealant is applied in liquid form and then cured by the use of a curing agent such as manganese dioxide.
F. Wilson, "Insulated Glass And Sealant Therefore," U.S. Pat. No. 4,153,594 (May 8, 1979) discloses polyurethane sealants prepared from a hydroxyl-terminated polybutadiene prepolymer and certain plasticizers.
C. Fryling, "Plasticizing Synthetic Rubber With A Reaction Product Of An Alkanethiol And A Rubbery Diolefin Polymer," U.S. Pat. No. 2,543,844 (March 1951) teaches the use of alkanethiol butadiene styrene adducts as plasticizers to increase the tack and decrease the hardness of synthetic rubber.
G. Serniuk, "Thioglycollic Acid Adducts Of Rubber-like Polymers And Process Of Preparing Same," U.S. Pat. No. 2,589,151 (Mar. 11, 1952) discloses that the hydrocarbon solvent resistance of polybutadiene is improved by partially saturating the double bonds of the polymer with thioglycollic acid. The polythioether adduct so prepared is insoluble in benzene, benzene/isopropyl alcohol, naptha, and carbon tetrachloride.
P. Warner, "Method Of Preparing Sealants From Polybutadiene And Mercapto Hydroxy Compounds," U.S. Pat. No. 3,689,450 (Sept. 5, 1972) teaches that mercaptohydroxy polybutadiene adducts cured with sulfur or sulfur donor compounds are thermally stable when exposed to ultraviolet light at 140.degree. F. and 50% relative humidity.
While the addition of alkanethiol to diene polymers is known to result in enhanced chemical properties such as thermal stability, solvent resistance, and oxidation resistance, attempts to commercialize these thioether-modified diene polymers and copolymers as sealant compositions have failed due to the objectionable odors these compounds give off.